Glazing panel

ABSTRACT

A glazing panel carrying a coating stack comprises in sequence at least:  
     a glass substrate  
     a base antireflective layer  
     an infra-red reflecting layer, and  
     a top antireflective layer  
     in which at least one of the antireflective layers comprises at least one mixed nitride layer which is a mixture of Al and at least one additional material X, in which the atomic ratio X/Al is greater than or equal to 0.05 and in which X is one or more of the materials selected from the group comprising the elements of Groups 3a, 4a, 5a, 4b, 5b, 6b, 7b, 8 of the periodic table. The glazing panel is particularly suitable for heat treatment and incorporation in windscreens.

[0001] This application is a continuation in part of U.S. patentapplication Ser. No. 09/466,784 filed Dec. 20, 1999, and incorporatedentirely herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to glazing panels and particularly, butnot exclusively, to solar control glazing panels which are intended toundergo heat treatment following application of a solar control filter.

[0004] 2. Discussion of Background

[0005] EP 233003 A describes a glazing panel carrying a sputter coatedoptical filter having the structure: glass substrate/ SnO₂ basedielectric/ first metallic barrier of Al, Ti, Zn, Zr or Ta/Ag/ secondmetallic barrier of Al, Ti, Zn, Zr or Ta/ SnO₂ top dielectric. Theoptical filter is designed to block a significant portion of theincident radiation in the infra red portion of the spectrum whilstallowing passage of a significant portion of the incident radiation inthe visible portion of the spectrum. In this way, the filter acts toreduce the heating effect of incident sunlight whilst allowing goodvisibility through the glazing and is particularly suitable for carwindscreens.

[0006] In this type of structure, the Ag layer acts to reflect incidentinfra red radiation and in order to fulfil this role must be maintainedas silver metal rather than silver oxide and must not be contaminated byadjacent layers. The dielectric layers which sandwich the Ag layer serveto reduce the reflection of the visible portion of the spectrum whichthe Ag layer would otherwise provoke. The second barrier serves toprevent oxidation of the Ag layer during sputtering of the overlyingSnO₂ dielectric layer in an oxidising atmosphere; this barrier is atleast partially oxidised during this process. The main role of the firstbarrier is to prevent oxidation of the silver layer during heattreatment of the coating (e.g. during bending and/or tempering) of theglazing panel by being oxidised itself rather than allowing passage ofoxygen to the Ag layer. This oxidation of the barrier during heattreatment provokes an increase in TL of the glazing panel.

[0007] EP 792847A discloses a heat treatable solar control glazing panelwhich is based on the same principle and has the structure: glasssubstrate/ ZnO dielectric/ Zn barrier/ Ag/ Zn barrier/ ZnO dielectric/Zn barrier/ Ag/ Zn barrier/ ZnO dielectric. The Zn barriers positionedbelow each of the Ag layers are intended to be oxidised completelyduring heat treatment and serve to protect the Ag layers from oxidation.As well known in the art, the structure of having two, spaced Ag layersrather than a single layer Ag layer increases the selectivity of thefilter.

[0008] EP 718250A discloses the use of a layer which provides a barrierto oxygen diffusion as at least part of the outermost dielectric layerin this type of filter stack. Such a layer must have a thickness of atleast 100 Å and preferably at least 200 Å in order to form an effectivebarrier and may comprise a silicon compound SiO2, SiOxCy, SiOxNy,nitrides like Si3N4 or AIN, carbides like SiC, TiC, CrC and TaC.

[0009] According to one aspect, the present invention provides a glazingpanel as defined in claim 1.

[0010] The antireflective layer is a layer composed of at least onemember selected from the group consisting of oxides, nitrides andcarbides and double compounds thereof.

[0011] As the oxide, for example, an oxide of at least one elementselected from the group consisting of Zn, Ti, Sn, Si, Al, Ta or Zr maybe mentioned. In addition, for example, zinc oxide containing Al, Ga, Sior Sn or indium oxide containing Sn may be mentioned.

[0012] As the nitride, a nitride of at least one element selected fromthe group consisting of Si, Al and B (a nitride (A)) or a mixture(inclusive of a double nitride) of a nitride of Zr or Ti with a nitride(A) may be mentioned.

[0013] As the double compound, SiO_(x)C_(y), SiO_(x)N_(y), SiAl_(x)N_(y)or SiAl_(x)O_(y)N_(z) may be mentioned. The antireflective layer may bea single layer or a multiple layer.

[0014] Especially, a zinc oxide or a zinc oxide containing at least oneelement selected from the group consisting of Sn, Al, Cr, Ti, Si, B, Mg,In and Ga is preferable, because it makes it possible to stably form anadjacent infra-red reflecting layer with a high crystallinity.Especially, a zinc oxide containing Al and/or Ti is preferable.

[0015] The infra-red reflecting material is a material that has areflectance higher than the reflectance of sodalime glass in the band ofwavelength between 780 nm and 50 μm.

[0016] The infra-red reflecting layer is a layer composed of Ag only ora layer comprising Ag as the main component and an additional metalelement (such as Pd, Au or Cu). When an additional metal element iscontained, the content of the additional metal element is preferablyfrom 0.3 to 10 at %, more preferably from 0.3 to 5 at %, based on thetotal of Ag and the additional metal element. If the content of anadditional metal element is less than 0.3 at %, the effect ofstabilizing Ag is small. Also, if the content of an additional metalelement exceeds 10 at %, the effect of stabilizing Ag diminishes.Especially, Pd as the additional metal element can immobilize Ag atoms,namely depress the migration of Ag atoms and affords a layer which isexcellent in stability and chemical resistance at high temperatures. Asthe Pd content increases, the rate of film formation tends to decrease,the visible light transmittance tends to lower, and the shieldingselectivity between visible rays and near infrared rays tends to becomepoor. Therefore, the Pd content (Pd/Ag) is preferred to be at most 5.0at %, especially from 0.3 to 2.0 at %, more preferably from 0.3 to 1.0at %.

[0017] When the glass laminate of the present invention comprises morethan one infra-red reflecting layer, each infra-red layer may have thesame composition or a different composition. The infra-red reflectinglayer may be a multiple layer comprising at least two laminated films,for example, a multiple layer composed of Ag and Pd.

[0018] In a glazing panel having a three layer type laminated coating,the thickness of the base antireflective layer, the infra-red layer andthe top antireflective layer layer are preferably from 15 to 45 nm, from9 to 16 nm (especially from 9 to 12 nm) and from 30 to 45 nm,respectively. A glazing panel comprising a colorless soda lime glasssubstrate of 2 mm thick and a three layer type laminated coating formedon the substrate has such representative optical properties as aluminous transmittance (TL) of about from 75 to 85% and an energetictransmittance (TE) of about from 50 to 70% after heat treatment.

[0019] In a glazing panel having a five layer type laminated coating,the thicknesses of the base antireflective layer, the infra-red layerthe central antireflective layer, the infra-red layer and the topantireflective layer layer are preferably from 16 to 50 nm (especiallyfrom 20 to 45 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm),from 40 to 100 nm (especially from 45 to 90 nm), from 6.5 to 16 nm(especially from 6.5 to 12.5 nm) and from 16 to 50 nm (especially from20 to 45 nm), respectively. A glazing panel comprising a colorless sodalime glass substrate of 2 mm thick and a five layer type laminatedcoating formed on the substrate has such representative opticalproperties as a luminous transmittance (TL) of about from 70 to 80% andan energetic transmittance (TE) of about from 40 to 50% after heattreatment.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The term “heat treatable glazing panel” as used herein means thatthe glazing panel carrying the coating stack is adapted to undergo abending and/or thermal tempering and/or thermal hardening operationand/or other heat treatment process without the haze of the so treatedglazing panel exceeding 0.5, and preferably without the haze exceeding0.3. The term “substantially haze free heat treated glazing panel” asused herein means a glazing panel carrying a coating stack which hasbeen bent and/or thermally tempered and/or thermally hardened and has ahaze that does not exceed 0.5 and which preferably does not exceed 0.3.In the present invention, a glazing panel can be subjected to heattreatment for 1) bending, 2) tempering, 3) sintering of colored ceramicprint or silver bus bar print, 4) vacuum sealing of vacuum doubleglazing and 5) calcination of a wet-coated low reflective coating orantiglare coating. For example, it is heated to a temperature of from570 to 700° C. in the atmosphere for 1) bending or 2) tempering. Thebending and/or thermal tempering and/or thermal hardening operation maybe carried out at a temperature of at least, 600° C. for at least 10minutes, 12 minutes, or 15 minutes , at least 620° C. for at least 10minutes, 12 minutes, or 15 minutes, or at least 640° C. for at least 10minutes, 12 minutes, or 15 minutes.

[0021] Any suitable method or combination of methods may be used todeposit the coating layers. For example, evaporation (thermal orelectron beam), liquid pyrolysis, chemical vapour deposition, vacuumdeposition and sputtering, particularly magnetron sputtering, the latterbeing particularly preferred. Different layers of the coating stack maybe deposited using different techniques.

[0022] The mixed nitride layer comprising aluminium may contain a “pure”nitride, an oxynitride, a carbonitride or an oxycarbonitride. The mixednitride layer comprising aluminium may be deposited by sputtering atarget in a nitrogen atmosphere. Alternatively, it may be deposited bysputtering a target in an atmosphere which is a mixture of argon andnitrogen.

[0023] The use of a mixed nitride comprising aluminium rather than pureor undoped AIN may be used to confer good resistance to oxidation and/ormoisture to the coating stack. This is particularly so when the mixednitride comprising aluminium forms part of the top antireflective layer,particularly when it forms the exposed layer.

[0024] A mixed nitride layer comprising aluminium in the baseantireflective layer is believed effective in blocking not only oxygenbut also sodium ions and other ions that can diffuse from the glass intothe coating stack and cause a deterioration of optical and electricalproperties, particularly if the glazing panel is subjected to heattreatment.

[0025] Particularly good results may be obtained when the additionalmaterial X is one or more of the materials selected from the groupcomprising Si, Zr, Hf, Ti, Nb and B, particularly Si or Si and Zr. Wherethe mixed nitride layer comprises Si, the atomic ratios may be: X/Al ofabout 0.2-4, especially 0.4-3.5.

[0026] SiO₂ and Al₂O₃ are known to be effective barriers to diffusion ofsodium ions in sputtered coating stacks. In addition to being easier,quicker and more cost effective to deposit by sputtering, it is believedthat a mixed nitride layer comprising aluminium as part of the basedielectric layer provides an effective barrier to both sodium ions andoxygen diffusion. Furthermore, it is believed that the mixed nitridelayer comprising aluminium may provide an effective diffusion barrier atsmaller geometrical thicknesses than that required using knownmaterials. For example, good thermal resistance with respect to ion andoxygen diffusion from the glass substrate may be conferred on thecoating stack by arranging the mixed nitride layer comprising aluminiumhaving a geometrical thickness of greater than 30 Å, for example,greater than or about 50 Å, 80 Å or 90 Å, as at least part of the baseantireflective layer particularly if the coating stack also includes abarrier layer, for example a metal or sub-oxide barrier layer,underlying the infra-red reflecting layer. Even in the absence of such abarrier layer underlying the infra-red reflecting layer, good thermalresistance with respect to ion and oxygen diffusion from the glasssubstrate may be conferred on the coating stack by arranging the mixednitride layer comprising aluminium having a geometrical thickness ofgreater than 30 Å, preferably greater than 50 Å, 80 Å or 90 Å, forexample, about 100 Å as at least part of the base antireflective layer.The mixed nitride layer comprising aluminium may confer advantageousproperties even if it is less than 195 Å thick.

[0027] The ability to block ion and oxygen diffusion from the glasssubstrate with a relatively thin layer provides great flexibility in thematerials and thickness that may be used for the other layers in thecoating stack.

[0028] Both Si₃N₄ and AlN take longer to deposit by common sputteringtechniques than oxides traditionally used in such coatings e.g. ZnO,SnO₂. The ability to provide good thermal stability with a relativelythin layer of a mixed nitride layer comprising aluminium thus alleviatesthe deposition of such a layer as a limiting factor in a depositionprocess.

[0029] The optical thickness of the antireflective layers andparticularly that of the top antireflective layer is critical indetermining the colour of the glazing panel. If a portion of anantireflective layer is oxidised, for example during heat treatment ofthe glazing panel then, particularly with Si₃N₄ (refractive index about2) the optical thickness can be modified as Si₃N₄ may be oxidised toSiO₂ (refractive index about 1.45). Where the antireflective layercomprises a mixed nitride layer comprising aluminium whose nitride has arefractive index of about 2.0, oxidation of a part of this to Al₂O₃(refractive index about 1.7) will have lesser effect upon the opticalthickness of the layer.

[0030] The ability to use a layer of a mixed nitride layer comprisingaluminium which is less than 100 Å in thickness to provide an effectivethermal barrier provides significant flexibility in the choice of theoverall structure of the top antireflective layer. The layer comprisinga mixed nitride layer comprising aluminium may be about 85 Å inthickness; this provides a combination of good thermal resistance andthickness. The layer comprising a mixed nitride layer comprisingaluminium may have a thickness of greater than or equal to about 50 Å,60 Å or 80 Å; its thickness may be less than or equal to about 85 Å, 90Åor 95 Å.

[0031] The preferred atomic ratios X/Al defined in the claims mayprovide a good combination of thermal resistance and chemical durabilityfor the coating stack, particularly when the addition material X is Si,Zr or Si and Zr.

[0032] Preferable X/Al is 0.2-4, especialy 0.4-3.5.

[0033] The coating stack may comprise a barrier layer overlying theinfra red reflecting layer and/or a barrier layer underlying the infrared reflecting layer. Such barriers may contain one or more metals andmay be deposited, for example, as metal oxides, as metal sub-oxides oras metals.

[0034] Further, in the invention, when a layer composed of an oxide or adouble compound containing an oxide such as an oxynitride is formed asan antireflective layer by reactive sputtering in an atmospherecontaining an oxidative gas, formation of such antireflective layerdirectly on the infra-red reflecting layer can fail to give a glazingpanel having desired optical and electrical properties because ofoxidation of the infra-red reflecting layer Therefore, it is preferredto form a metal or nitride barrier layer. Such a barrier layer usuallystays in a partly oxidized state, and during heat treatment, oxidizesinto a transparent oxide having a higher visible light transmittance.

[0035] As the barrier layer, a metal of at least one element selectedfrom the group consisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr,Ni, Ni—Ti, a nitride of at least one element selected from the groupconsisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr, Ni, Ni—Ti, and asub-oxide (i.e. partially oxized) of at least one element selected fromthe group consisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr, Ni,Ni—Ti is preferable. The thickness of a barrier layer is preferably from1 to 5 nm. A barrier layer thinner than 1 nm does not work well, while abarrier layer thicker than 5 nm can lower the visible lighttransmittance of the glass laminate or cause other problems.

[0036] When an oxide layer, for example, composed of zinc oxidecontaining Al is formed directly on the infra-red reflecting layer asthe antireflective layer, an Al—Zn alloy barrier layer having the samemetal ratio can strengthen the adhesion between the infra-red reflectinglayer and the antireflective layer and thus is effective in improvingdurability of the layers of the multilayer structure. An Al—Zn alloybarrier layer is also preferable in view of the crystallinity of Ag inthe infra-red reflecting layer and the heat resistance. A barrier layermay be formed under the infra-red reflecting layer, too.

[0037] Providing a layer of a metal oxide between the mixed nitridelayer comprising aluminium and the infra-red reflecting material(particularly when this is silver or a silver alloy) may combine thethermal stability properties of the mixed nitride layer comprisingaluminium with an interposed material which favours crystallisation ofthe infra-red reflecting material so as to balance the infra redreflecting properties with the haze of the coating stack, particularlywhen it is subjected to heat treatment. One preferred such oxide is amixed oxide of zinc and aluminium, preferably with a Al/Zn atomic ratioof about 0.1. One possible explanation for this may be that the presenceof the Al in the zinc oxide structure may reduce the crystal graingrowth in the mixed oxide layer.

[0038] The effectiveness of a relatively thin layer of the mixed nitridelayer comprising aluminium in conferring thermal stability allows use ofa relatively thick layer of such an oxide.

[0039] Heat treatment may provoke an increase in the TL of the glazingpanel. Such an increase in TL may be advantageous in ensuring that TL issufficiently high for the glazing panel to be used in a vehiclewindscreen. TL may increase in absolute terms during heat treatment by,for example, greater than about 2.5%, greater than about 3%, greaterthan about 5%, greater than about 8% or greater than about 10%.

[0040] According to a farther aspect, the present invention provides amethod of manufacturing a glazing panel as defined in claim 16. Thisprovides a heat treated glazing panel having a haze of less than about0.5 and preferably less than about 0.3 suitable for use, for example, inarchitectural, vehicle and industrial applications.

[0041] Examples of the present invention will now be described withreference to FIG. 1 which is a cross-section through a glazing panelprior to a bending and tempering operation (for ease of representation,the relative thicknesses of the glazing panel and coating layers are notshown to scale).

EXAMPLE 1

[0042]FIG. 1 shows a double Ag layer, heat treatable, coating layerdeposited on a glass substrate by magnetron sputtering and having thefollowing sequential structure: Reference Geometrical number thicknessAtomic ratios Glass substrate 10  2 mm Base dielectric comprising: 11AlSixNy 12  40 Å Si/Al = 0.5 ZnAlOx 13 260 Å Al/Zn = 0.1 ZnAlOyunderlying barrier 14  10 Å Al/Zn = 0.1 Ag 15 100 Å ZnAlOy overlyingbarrier 16  12 Å Al/Zn = 0.1 Central dielectric comprising ZnAlOx 17 770Å Al/Zn = 0.1 ZnAlOy underlying barrier 18  7 Å Al/Zn = 0.1 Ag 19 100 ÅZnAlOy overlying barrier 20  17 Å Al/Zn = 0.1 Top dielectric comprising:ZnAlOx 22 185 Å Al/Zn = 0.1 AlSixNy 23  75 Å Si/Al = 0.3

[0043] AlSixNy is a mixed nitride containing Al and Si deposited in thisexample by reactively sputtering a mixed target containing Al and Si inthe presence of nitrogen and argon.

[0044] ZnAlOx is a mixed oxide containing Zn and Al deposited in thisexample by reactively sputtering a target which is an alloy or mixtureof Zn and Al in the presence of oxygen . The ZnAlOy barriers aresimilarly deposited by sputtering a target which is an alloy or mixtureof Zn and Al in an argon rich oxygen containing atmosphere to deposit abarrier that is not fully oxidised.

[0045] Alternatively, the mixed oxide layer ZnAlOx may be formed bysputtering a target which is a mixture of zinc oxide and an oxide of Al,particularly in an argon gas or argon rich oxygen containing atmosphere.

[0046] Where the barrier layers comprise the same materials as the mixedoxide layer, particularly the adjacent mixed oxide layer, this mayfacilitate management of targets and control of deposition conditionsand may provide good adhesion between the layers and thus goodmechanical durability of the coating stack.

[0047] The oxidation state in each of the base, central and top ZnAlOxdielectric layers need not necessarily be the same. Similarly, theoxidation state in each of the ZnAlOy barriers need not be the same.Equally, the Al/Zn ratio need not be the same for all of the layers; forexample, the barrier layers may have a different Al/Zn ratio to theantireflective dielectric layers and the antireflective dielectriclayers may have different Al/Zn ratios from each other.

[0048] Each overlying barrier protects its underlying silver layer fromoxidation during sputter deposition of its overlying ZaAlOx oxide layer.Whilst further oxidation of these barriers layers may occur duringdeposition of their overlying oxide layers a portion of these barrierspreferably remains in the form of an oxide that is not fully oxidised toprovide a barrier for subsequent heat treatment of the glazing panel.

[0049] This particular glazing panel is intended for incorporation in alaminated vehicle windscreen and displays the following properties:Prior to heat Following heat treatment^(see Note 1)treatment^(see Note 2) Property ^(below) ^(below) TL(Illuminant A) 65%76% TE (System Moon 2) 40% 43% haze 0.1 0.2 a* −15 (coated side) −2(external) b* +1 (coated side) −10 (external) RE (System Moon 2) 29%(coated side) 31% (external)

[0050] Heat treatment preferably causes substantially complete oxidationof all of the barrier layers such that the structure of the coatingstack after heat treatment is: Reference Geometrical number thicknessAtomic ratios Glass substrate 10  2 mm Base dielectric comprising: 11AlSixNy (partially 12  40 Å Si/Al = 0.5 oxidised) ZnAlOx 13 260 Å Al/Zn= 0.1 ZnAlOx (oxidised underlying 14 10 Å-16 Å Al/Zn = 0.1 barrier) Ag15 100 Å ZnAlOx (oxidised overlying 16 14 Å-20 Å Al/Zn = 0.1 barrier)Central dielectric comprising ZnAlOx 17 770 Å Al/Zn = 0.1 ZnAlOx(oxidised underlying 18  7 Å-12 Å Al/Zn = 0.1 barrier) Ag 19 100 ÅZnAlOx (oxidised overlying 20 20 Å-28 Å Al/Zn = 0.1 barrier) Topdielectric comprising: ZnAlOx 22 185 Å Al/Zn = 0.1 AlSixNy (partiallyoxidised) 23  75 Å Si/Al = 0.3

[0051] The AlSixNy (partially oxidised) layers may comprise a mixture ofAIN, Si₃N₄, Al₂O₃ and SiO₂, the AlSixNy being partially oxidised duringthe heat treatment process. The barrier layers are not necessarilycompletely oxidised and their thickness will depend to a certain extentupon their degree of oxidation.

EXAMPLE 2

[0052] Example 2 is similar to Example 1, save that the underlyingbarriers of the coating stack were omitted. The coating stacks andproperties of the Example are set out below: Reference Geometricalnumber thickness Atomic ratios Glass substrate 10  2 mm Base dielectriccomprising: 11 AlSixNy 12  85 Å Si/Al = 0.8 ZnAlOx 13 240 Å Al/Zn = 0.1Ag 15 100 Å ZnAl overlying barrier 16  10 Å Al/Zn = 0.1 Centraldielectric comprising ZnAlOx 17 800 Å Al/Zn = 0.1 Ag 19 115 Å ZnAloverlying barrier 20  15 Å Al/Zn = 0.1 Top dielectric comprising: ZnAlOx22 150 Å Al/Zn = 0.1 AlSixNy 23  80 Å Si/Al = 0.8

[0053] At least a portion of the overlying barriers 16, 20 is oxidisedduring deposition of their overlying oxide layers. Nevertheless, aportion of these barriers preferably remains in metallic form, or atleast in the form of an oxide that is not fully oxidised to provide abarrier for subsequent heat treatment of the glazing panel.

[0054] This particular glazing panel is intended for incorporation in alaminated vehicle windscreen and displays the following properties:Prior to heat Following heat treatment^(see Note 1)treatment^(see Note 2) Property ^(below) ^(below) TL (Illuminant A) 67%77% TE (System Moon 2) 38% 44% haze 0.1 0.21 a* −10 (coated side) −3(external) b* +18 (coated side) −7 (external) RE (System Moon 2) 27%(coated side) 32% (external)

[0055] Heat treatment preferably causes substantially complete oxidationof all of the barrier layers such that the structure of the coatingstack after heat treatment is:

[0056] Coating stack following heat treatment Reference Geometricalnumber thickness Atomic ratios Glass substrate 10  2 mm Base dielectriccomprising: 11 AlSixNy (partially 12  85 Å Si/Al = 0.8 oxidised) ZnAlOx13 240 Å Al/Zn = 0.1 Ag 15 100 Å ZnAlOx (oxidised overlying 16 12-20 ÅAl/Zn = 0.1 barrier) Central dielectric comprising ZnAlOx 17 800 Å Al/Zn= 0.1 Ag 19 115 Å ZnAlOx (oxidised overlying 20 17-30 Å Al/Zn = 0.1barrier) Top dielectric comprising: ZnAlOx 22 150 Å Al/Zn = 0.1 AlSixNy(partially oxidised) 23  80 Å Si/Al = 0.8

EXAMPLES 3

[0057] The coating stack of Example 3 is set out below Geometricalthickness Atomic ratios Glass substrate 2 mm Base dielectric comprising:AlSixNy 100 Å Si/Al = 3 ZnAlOx 230 Å Al/Zn = 0.03 Ag doped with 1 at %palladium  95 Å ZnAl overlying barrier  20 Å Al/Zn = 0.03 Centraldielectric comprising ZnAlOx 750 Å Al/Zn = 0.03 Ag doped with 1 at %palladium  95 Å ZnAl overlying barrier  20 Å Al/Zn = 0.03 Top dielectriccomprising: ZnAlOx 230 Å Al/Zn = 0.03 AlSixNy 100 Å Si/Al = 3

[0058] Samples having this coating stack were stored for seven days,some samples being stored in a dry atmosphere and others in a humidatmosphere at 40° C. with 90% relative humidity. The samples weresubsequently heat treated with a maximum temperature of 630° C. tosimulate glass bending. The results are set out below, the opticalproperties being measured just before and just after heat treatment:Stored in dry Stored in humid atmosphere atmosphere TL(prior to heattreatment) 64.7% 64.9% TE prior to heat treatment) 36.4% 36.6%haze(prior to heat treatment)  0.1  0.1 TL (after heat treatment) 77.7%77.1% TE (after heat treatment) 48.6% 47.7% Haze (after heat treatment) 0.2  0.2 RS (after heat treatment)  5.8 ohm/sq.  5.9 ohm/sq.

EXAMPLE 4 (Comparative Example)

[0059] For Example 4, the coating stack of Example 3 was used, save thatthe AlSixNy layers were replaced with undoped aluminium nitride AIN. Theresults following the same tests were Stored in dry Stored in humidatmosphere atmosphere TL (prior to heat treatment) 67.2% 67.2% TE (priorto heat treatment) 37.8% 37.4% haze(prior to heat treatment)  0.1  0.1TL (after heat treatment) 77.3% 76.8% TE (after heat treatment) 46.7%47.4% Haze (after heat treatment)  0.3  1.2 RS (after heat treatment) 5.9 ohm/sq.  6.1 ohm/sq.

[0060] Examples 3 shows the improvement of the resistance to severelyhumid atmospheres of the mixed nitride comprising aluminium (containingsilicon in this case) when compared with “pure” AlN.

[0061] Particularly unacceptable haze after heat treatment followingstorage in a humid atmosphere is observed in Example 4.

EXAMPLES 5 TO 8

[0062] The coating stack of Examples 5 to 8 is set out below Geometricalthickness Atomic ratios Glass substrate  2 mm Base dielectriccomprising: AlSixNy 100 Å Si/Al = 3 ZnAlOx 230 Å Al/Zn = 0.03 Ag dopedwith 1 at % palladium 100 Å ZnAl overlying barrier  20 Å Al/Zn = 0.03Central dielectric comprising ZnAlOx 750 Å Al/Zn = 0.03 Ag doped with 1at % palladium 100 Å ZnAl overlying barrier  20 Å Al/Zn = 0.03 Topdielectric comprising: ZnAlOx varies Al/Zn = 0.03 AlSixNy Si/Al = 3

[0063] In these examples, the properties of the glazing were measuredprior to heat treatment and after heat treatment with a maximumtemperature of 630° C. to simulate glass bending for differentthicknesses of the layers of the top dielectric. The results are set outbelow: The composition of the top dielectric layers in these exampleswas: Example ZnAlOx AlSixNy 5 220 Å 110 Å  6 245 Å 85 Å 7 270 Å 60 Å 8295 Å 35 Å

[0064] and the results were Example 5 6 7 8 TL (as deposited) 64.3% 65%65.2% 64.5% RV (as de osited) 6.5%  6.5% 6.5% 6.4% TE (as deposited)35.5% 36.4% 36.5% 3 5.9% RE (as deposited) 35% 33.7% 33.6 % 33.7% TL(after heat treatment) 76.8% 76.8% 77.1% 76.8% RV (after heat treatment) 9.1% 7.5% 7.5% 7.6% TE (after heat treatment) 47.3% 46.5% 46.9% 46.9%RE (after heat treatment) 36.3    36.5 35.8 35.8 Haze (after heattreatment)  0.2    0.2 0.2 0.2 note OK OK OK OK

EXAMPLES 9 TO 12

[0065] The coating stack of Examples 9 to 12 is set out belowGeometrical thickness Atomic ratios Glass substrate 2 mm Base dielectriccomprising: a nitride layer 100 Å ZxAlOx 230 Å Al/Zn = 0.03 Ag dopedwith 1 at % palladium 100 Å ZnAl overlying barrier  20 Å Al/Zn = 0.03Central dielectric comprising ZnAlOx 750 Å Al/Zn = 0.03 A doped with 1at % palladium 100 Å ZnAl overlying banier  20 Å Al/Zn = 0.03 Topdielectric comprising ZnAlOx 230 Å Al/Zn = 0.03 a nitride layer 100 Å

[0066] The composition of the nitride layer in the base dielectic andtop dielectic layers in these examples was: nitride layer in basenitride layer in top Example dielectric dielectric  9 AlN AlN 10 AlNAlSixNy Si/Al = 3 11 AlSixNy AlN Si/Al = 3 12 AlSixNy AlSixNy Si/Al = 3

[0067] Using these examples, comparative tests were carried out storingthe samples in dry conditions and in the humid conditions of theprevoius examples and subsequently subjecting the samples to a heattreatment at 630° C. The results are set out below Storage in dryconditions: Example 9 10 11 12 TL (prior to heat treatment) 64.9% 63.5%64.4% 63.3% RV (prior to heat treatment) 7.7% 6.2% 6.5% 8.4% TE (priorto heat treatment) 36.2% 34.7% 35.3% 34.6% RE (prior to heat treatment)32.9% 33.3% 33.2% 34.6% TL (after heat treatment) 75.8% 76.7% 76.3%75.9% RV (after heat treatment) 7.9% 7.7% 7.2% 8.5% TE (after heattreatment) 44.9% 47.1% 44.3% 44.5% RE (after heat treatment) 36.3% 34.1%37.3% 36.4% Haze (after heat treatment) 0.4 0.3 0.4 0.4 note OK OK OK OK

[0068] Storage in humid conditions: Example 9 10 11 12 TL (prior to heattreatment) 66.0% 64.8% 65.3% 63.7% RV (prior to heat treatment) 7.8%6.6% 7.0% 8.8% TE (prior to heat treatment) 37.0% 35.9% 36.1% 35.1% RE(prior to heat treatment) 32.6% 32.2% 32.4% 33.9% TL (after heattreatment) 75.3% 76.4% 76.4% 75.3% RV (after heat treatment) 8.5% 7.5%7.4% 8.0% TE (after heat treatment) 45.4% 46.9% 45.0% 43.8% RE (afterheat treatment) 35.7% 33.1% 37.3% 36.1% Haze (after heat treatment) 0.80.6 0.4 0.4 note large haze haze OK OK spots

[0069] These examples illustrate the use of mixed AlSixNy layers as partof the base dielectric and as part of the top dielectric and comparisonwith “pure” AIN. They also illustrate that the use of AlSixNy isparticularly advantageous when used in the base dielectric layer,especially when the glazing panel is stored in a severely humidatmosphere.

[0070] Additional layers may be introduced above, below or between thefilm stacking arrangement if desired without departing from theinvention.

[0071] In addition to the advantageous optical properties that may beobtained, each of the examples provides a coating layer which may beelectrically heated, for example, in an electrically heated carwindscreen to provide a de-misting and/or de-frosting function with theaddition of suitably placed electrical connectors.

[0072] The colour co-ordinates of the examples are particularly suitedto car windscreens as they give a neutral or slightly blue or slightlygreen appearance in reflection when the windscreen is mounted at anangle in the car body. For other applications, for example architecturalapplications, the colour in reflection may be adjusted as is known inthe art by adjusting the thicknesses of the dielectric layers and/orinfra red reflecting layer(s).

[0073] The TL of the glazing panel may be adjusted to suit the desiredapplication. For example

[0074] if the glazing panel is to be used as a windscreen for theEuropean market, TL may be selected to be greater than 75% (as requiredby European regulations).

[0075] if the glazing panel is to be used as a windscreen for the Japanand US market, TL may be selected to be greater than 70% (as required byJapan and US regulations).

[0076] if the glazing panel is to be used as a vehicle front sidelight,TL may be adjusted to be greater than 70% (as required by Europeanregulations).

[0077] if the glazing panel is to be used as a vehicle rear sidelight ora rear window for a vehicle, TL may be selected to be between about 30%and 70%.

[0078] Such adjustment of TL may be achieved, for example,

[0079] by adapting the thicknesses of the layers of the coating stack,in particular the thicknesses of the dielectric layers and/or theinfra-red reflecting layer(s).

[0080] by combining the coating stack with a tinted glass substrate, forexample, in order to increase the selectivity.

[0081] by combining the coating stack with a tinted pvb or otherlaminating layer.

GLOSSARY

[0082] Unless otherwise indicated by the context, the terms listed belowhave the following meanings in this specification: a* colour co-ordinatemeasured on the CIELab scale at normal incidence Ag silver Al aluminiumAl2O3 aluminium oxide AlN aluminium nitride b* colour co-ordinatemeasured on the CIELab scale at normal incidence B boron Bi bismuth Crchromium haze the percentage of transmitted light which in passingthrough the specimen deviates from the incident beam by forwardscattering, as measured in accordance with the ASTM Desingation D1003-61 (reapproved 1988). Hf hafrium infra red a material that has arelfectance higher than the reflectance of sodalime glass in reflectingthe band of wavelengths between 780 nm and 50 microns material Na sodiumNb niobium NCr an alloy or mixture comprising nickel and chromium NTi analloy or mixture comprising nickel and titanium RE energetic the solarflux (luminous and non-luminous) reflected from a substrate as areflection percentage of the incident solar flux RS sheet resistancemeasured by four point probe method RV luminous reflectance Sb antimonyselectivity the ratio of the luminous transmittance to the solar factori.e. TL/TE SiO2 silicon oxide Si3N4 silicon nitride SnO2 tin oxide Tatantalum TE energetic the solar flux (luminous and non-luminous)transmitted through a substrate as a transmittance percentage of theincident solar flux Ti titarium TL luminous the luminous fluxtransmitted through a substrate as a percentage of the incidenttransmittance luminous flux Zn zinc ZnAl an alloy or mixture comprisingzinc and aluminium ZnAlOx a mixed oxide containing zinc and aluminiumZnAlOy a partially oxidised mixture comprising zinc and aluminium ZnOzinc oxide ZnTi an alloy or mixture comprising zinc and titarium ZnTiOxa mixed oxide containing zinc and titarium ZnTiOy a partially oxidisedmixture comprising zinc and titarium Zr zirconium

What is claimed is:
 1. A glazing panel carrying a coating stackcomprising in sequence at least: a glass substrate a base antireflectivelayer an infra-red reflecting layer, and a top antireflective layercharacterised in that at least one of the antireflective layerscomprises at least one mixed nitride layer which is a mixture of Al andat least one additional material X, in which the atomic ratio X/Al isgreater than or equal to 0.05 and in which X is one or more of thematerials selected from the group comprising the elements of Groups 3a,4a, 5a, 4b, 5b, 6b, 7b, 8 of the periodic table.
 2. A glazing panel inaccordance with claim 1 comprising in sequence at least: a glasssubstrate a base antireflective layer an infra-red reflecting layer acentral antireflective layer an infra-red reflecting layer a topantireflective layer characterised in that at least one of theantireflective layers comprises at least one mixed nitride layer whichis a mixture of Al and at least one additional material X, in which theatomic ratio X/Al is greater than or equal to 0.05 and in which X is oneor more of the materials selected from the group comprising the elementsof Groups 3a, 4a, 5a, 4b, 5b, 6b, 7b, 8 of the periodic table.
 3. Aglazing panel in accordance with claim 1 or claim 2, in which X is oneor more of the materials selected from the group comprising Si, Zr, Hf,Ti, Nb and B.
 4. A glazing panel in accordance with any preceding claim,in which the glazing panel is a heat treatable or substantially hazefree heat treated glazing panel.
 5. A glazing panel in accordance withany preceding claim, in which the at least one mixed nitride layer has ageometrical thickness greater than or equal to than 30Å.
 6. A glazingpanel in accordance with any preceding claim, in which the at least onemixed nitride layer has a geometrical thickness less than 195 Å.
 7. Aglazing panel in accordance with any preceding claim, in which the atleast one mixed nitride layer has a geometrical thickness of less than100 Å and forms at least part of the top antireflective layer.
 8. Aglazing panel in accordance with any preceding claim, in which each ofthe base antireflective layer and the top antireflective layer comprisesat least one mixed nitride layer which is a mixture of Al and at leastone additional material X, in which the atomic ratio X/Al is greaterthan or equal to 0.05 and in which X is one or more of the materialsselected from the group comprising the elements of Groups 3a, 4a, 5a,4b, 5b, 6b, 7b, 8 of the periodic table.
 9. A glazing panel inaccordance with any one of claims 2 to 8, in which the centralantireflective layer comprises at least one mixed nitride layer which isa mixture of Al and at least one additional material X, in which theatomic ratio X/Al is greater than or equal to 0.05 and in which X is oneor more of the materials selected from the group comprising the elementsof Groups 3a, 4a, 5a, 4b, 5b, 6b, 7b, 8 of the periodic table.
 10. Aglazing panel in accordance with any preceding claim, in which theatomic ratio X/Al of the mixed nitride layer is within the range0.05-20.
 11. A glazing panel in accordance with any preceding claim, inwhich the atomic ratio X/Al of the mixed nitride layer is within therange 0.2-4.
 12. A glazing panel in accordance with any preceding claim,in which the atomic ratio X/Al of the mixed nitride layer is within therange 0.4-3.5.
 13. A glazing panel in accordance with any precedingclaim, in which the base antireflective layer comprises a layer adjacentto the substrate comprising the mixed nitride layer, and an overlyinglayer comprising a mixed oxide layer which comprises an oxide which is amixture of Zn and at least one additional material X, in which theatomic ratio X/Zn is greater than or equal to 0.03 and in which X is oneor more of the materials selected from the group comprising the elementsof Groups 2a, 3a, 5a, 4b, 5b, 6b of the periodic table.
 14. A glazingpanel in accordance with any preceding claim, in which the topantireflective layer comprises a mixed oxide layer which comprises anoxide which is a mixture of Zn and at least one additional material X,in which the atomic ratio X/Zn is greater than or equal to 0.03 and inwhich X is one or more of the materials selected from the groupcomprising the elements of Groups 2a, 3a, 5a, 4b, 5b, 6b of the periodictable, and an overlying layer comprising the mixed nitride layer.
 15. Aglazing panel in accordance with any preceding claim, in which theglazing panel is a heat treatable or substantially haze free heattreated glazing panel and in which heat treatment of the heat treatableglazing panel to form the substantially haze free heat treated glazingpanel provokes an increase of the value of TL of the glazing panel of atleast 2.5%.
 16. A method of manufacturing a glazing panel having a hazeof less than about 0.5 comprising the step of subjecting a glazing panelin accordance with any preceding claim to a heat treatment process at atleast 570° C.